The Gifford-McMahon (G-M) type pulse tube refrigerator is a cryocooler, similar to G-M refrigerators, that derives cooling from the compression and expansion of gas. However, unlike the G-M systems, in which the gas expansion work is transferred out of the expansion space by a solid expansion piston or displacer, pulse tube refrigerators have no moving parts in their cold end, but rather an oscillating gas column within the pulse tube that functions as a compressible displacer. The elimination of moving parts in the cold end of pulse tube refrigerators allows a significant reduction of vibration, as well as greater reliability and lifetime, and is thus potentially very useful in cooling cryopumps, which are often used to purge gases from semiconductor fabrication vacuum chambers.
G-M type pulse tube refrigerators are characterized by having a compressor that is connected to a remote expander by high and low pressure gas lines. The pulse tube expander has a valve mechanism that alternately pressurizes and depressurizes the regenerators and pulse tubes to produce refrigeration at cryogenic temperatures.
A Cryopump cooled by a Pulse Tube refrigerator needs to be quickly regenerated to minimize the time it is out of service. At present heaters are being used with GM refrigerators to rapidly warm up the cryopanels. Heaters can also be used to warm up cryopumps that are cooled by pulse tubes e.g. as disclosed in Japanese patent 00283036. When using a pulse tube to cool the cryopanels, warm up can also be achieved without heaters by circulating gas through the pulse tube, such as described in U.S. Pat. No. 5,927,081.
It is the object of the present invention to provide an improved means of quickly warming a pulse tube.